(1) Field of the Invention
The present invention relates to a deflection yoke of a cathode ray tube used for televisions and computer displays, and in particular to a deflection yoke having a bend-up-less saddle-type deflection coil as a horizontal or vertical deflection coil.
(2) Related Art
As an image display device in computers and televisions, a color cathode ray tube with a deflection yoke provided around a funnel has been widely used.
A general deflection yoke includes a pair of horizontal coils around the funnel, a pair of vertical coils on a funnel-shaped insulating frame positioned over the horizontal coils, and a coned ferrite core covering an outer surface of the vertical coils.
The pair of horizontal coils is positioned so that their windows face with each other in a vertical direction across a horizontal plane that includes a tube axis. Each horizontal deflection coil is symmetrical with respect to a vertical plane that includes the tube axis. The horizontal coils generate vertical magnetic fields to horizontally deflect electron beams. Also, the pair of the vertical coils is positioned so that their windows face with each other in a horizontal direction across the vertical plane that includes the tube axis. Each vertical deflection coil is symmetrical with respect to the horizontal plane that includes the tube axis. The vertical coils generate horizontal magnetic fields to vertically deflect electron beams. In this specification, xe2x80x9cvertical directionxe2x80x9d and xe2x80x9chorizontal directionxe2x80x9d refer to a vertical direction (a Y-axis direction) and a horizontal direction (an X-axis direction) of a screen of a cathode-ray tube. Also, xe2x80x9cvertical planexe2x80x9d and xe2x80x9chorizontal planexe2x80x9d refer to a plane extending vertically that includes the tube axis (YZ plane) and a plane extending horizontally that includes the tube axis (XZ plane).
Most of the horizontal and vertical coils are saddle-shaped coils curving substantially along the outer surface of the funnel.
As shown in FIGS. 5A, 5B and 10, a saddle-type coil includes a pair of cone parts 132 (232), a screen-side bend part 131 (231) connecting the pair of cone parts 132 (232) facing towards a screen, and an electron gun-side bend part 133 (233) connecting the pair of cone parts facing towards an electron gun.
Saddle-type coils are divided into xe2x80x98bend-upxe2x80x99 types and xe2x80x98bend-up-lessxe2x80x99 types, depending on whether the electron gun-side bend part 3 protrudes or not. A saddle-type coil 111a as shown in FIGS. 5A and 5B is a xe2x80x98bend-up-lessxe2x80x99 type in which the electron gun-side bend part 133 is extending along the outer surface of the funnel (not shown in the drawing). Meanwhile, a saddle-type coil 211 shown in FIG. 10 is a xe2x80x98bend-upxe2x80x99 type in which the electron gun-side bend part 233 protrudes (extends away) from the outer surface of the funnel.
The xe2x80x98bend-up-lessxe2x80x99 saddle-type coil has the electron gun-side bend part extending at a position closer to the tube axis, which makes it easy to suppress the strength of magnetic fields generated near the electron gun-side bend part. This means that the use of a deflection yoke with bend-up-less saddle-type coils has an effect of forming a more preferable distribution of principal magnetic fields than when using a deflection yoke with bend-up saddle-type coils therein. This will lead to a reduction in deflection power.
In general, there is a demand to lower power consumption of electric appliances. Accordingly, a reduction in deflection power consumption is required for color cathode-ray tubes having deflection yokes with the xe2x80x98bend-up-lessxe2x80x99 saddle-type coils.
Given the fact that deflection power is reduced as the distance between electron beams and coils or between the electron beams and the ferrite core is shorten, the deflection power can be reduced by making the horizontal coils and the vertical coils as thin as possible and setting the internal diameter of the ferrite core as short as possible.
In designing the bend-up-less saddle-type coils, however, a distribution of principal deflection magnetic fields largely determines the shape and number of turns of the coils and the coils that are commonly used do not vary much in diameter. For these reasons, the thickness of the coils is predetermined in effective.
For instance, in the electron gun-side bend part 133 of FIGS. 5A and 5B, the front-end location for a front part of the electron gun-side bend part 133 (an end facing towards the screen, which is represented by coordinate Z1 in FIGS. 5A and 5B) and the back-end location for a back part of the electron gun-side bend part (an end facing towards the electron gun, which is represented by coordinate Z2 in FIGS. 5A and 5B) serve as parameters in determining a distribution of principal deflection magnetic fields and a deflection center in the deflection yoke. The distribution in turn determines a raster characteristic and neck shadow tolerance of a color cathode-ray tube (coordinate Z1 and Z2 shown in FIGS. 5A and 5B are taken along the tube axis. The origin (Z=0) is taken so as to correspond with a point on a reference line, with a plus region being on the side of the screen and a negative region being on the side of the electron gun).
Therefore, if, in designing the deflection yoke, an optimal raster characteristic and a neck shadow tolerance are considered for each shape of funnels, the front-end location Z1 and the back-end location Z2 will be determined accordingly.
When the front-end location Z1, the back-end location Z2 and the number of turns of the coils are determined, a minimum thickness of the coils of the electron gun-side bend part 133 is determined. For instance, if n1 of copper wires having an outer diameter of 2r are wound n2 times, the number of turns of the copper coil to be obtained is n1xc2x7n2. Thus, the gross cross section area of the copper wires at the electron gun-side bend part 133 is xcfx80r2xc3x97n1xc2x7n2 and the thickness of the electron gun-side bend part 133 exceeds xcfx80r2xc3x97n1xc2x7n2/(Z2xe2x88x92Z1).
To realize an energy-efficient color cathode-ray tube, deflection power is reduced for a deflection yoke that includes one or more bend-up-less saddle type coils in at least one of a horizontal deflection coil and a vertical deflection coil, without changing a basic setting, which has an effect on deflection, such as a cross section area of the cone parts and a deflection center location. To do so, a horizontal deflection coil of a bend-up-less saddle shape has a protruding part protruding towards an electron gun at an electron gun-side bend part. Each side of the protruding part in a direction perpendicular to the tube axis is located at a point so that a vertical line drawn from the point to a tube axis forms an angle xcex1 of 10xc2x0 to 50xc2x0 inclusive with a vertical plane.
The ends of the protruding part in a direction perpendicular to the tube axis are the widest, and the bottom part of the protruding part is usually the widest. Therefore, the word xe2x80x9cside of the protruding part in a direction perpendicular to the tube axisxe2x80x9d refers to the bottom side of the protruding part, in other words, a point where the protruding part begins.
With this construction, the thickness of the coils of the electron gun-side bend part is reduced by the amount of the protruding part. The smaller the thickness of the electron gun-side bend part becomes, the smaller an inside diameter of the deflection yoke core can be, which covers the electron gun-side bend part. This will result in reducing deflection power requirement.
The protruding part is created only in an area where an angle formed between the vertical plane and the perpendicular line drawn to the tube axis is no greater than 50xc2x0, the position of the front-end location Z1 and back-end location Z2 of the electron gun-side bend part and the pattern of magnetic fields generated by the coils are not affected by whether the protruding part is created or not.
For a vertical deflection coil having a bend-up-less saddle shape, the protruding part can be formed at the electron gun-side bend part so that the protruding part protrudes towards the electron gun and that each side of the protruding part that is perpendicular to the tube axis is located at a point such that a perpendicular line drawn from the point to the tube axis forms an angle of 10xc2x0 to 50xc2x0 with a horizontal plane.
As the horizontal deflection coil experiences, thickness of the electron gun-side bend part of the vertical deflection coil can be reduced, and thus the deflection power can be reduced while maintaining the front-end location Z1 and back-end location Z2 of the electron gun-side bend part at the same position as they are when the protruding part is not created.
Such a protruding part can be easily formed by press molding a part of the horizontal or vertical deflection coil.
It is preferable that the protruding part has a rectangular shape and is no less than 3 mm in length.